Ammonia storage and injection in NOx control

ABSTRACT

A system is described for storing ammonia and injecting it into the exhaust gas stream of an engine to reduce nitrogen oxides. The ammonia is stored as a liquid mixture ( 70 ) of ammonia and water in a container ( 50 ). In one system, the mixture passes through a hot nozzle and is injected into an upstream portion of the exhaust gas pipe.

CROSS-REFERENCE

This is a continuation-in-part of Ser. No. 10/132,552 filed Apr. 24,2002.

BACKGROUND OF THE INVENTION

In our earlier U.S. Pat. Nos. 5,224,346 and 5,992,141, we describedexperiments which showed that the amount of nitrogen oxides (NO andNO₂), or NOx in engine exhaust gasses can be reduced by injectingammonia (NH₃) which reacts with nitrogen oxides to produce nitrogen andwater. One practical problem is how to store ammonia that is to beinjected into the exhaust gas stream. Ammonia can be stored as a liquid,at a pressure of about 150 psi, with the ammonia turning into gas whenremoved from the container and its pressure reduced. It is oftenundesirable to store ammonia under considerable pressure because of thedanger of an explosion and the possibility of rapid leakage of ammonia.Another way for storing ammonia is to store it as urea (H₂ NCO NH₂) asin a solution with water, and inject it into the exhaust gas stream.However, it can take a longer time for urea to react with nitrogenoxides and turn them into nitrogen and water, than ammonia. Since thetemperature of the exhaust gas stream very rapidly drops as the exhaustgasses move through the exhaust pipe into the atmosphere, it isdesirable that the reactions occur very rapidly so they can occur at thehigh temperatures that exist in and near the exhaust gas manifold sothat a high proportion of the injected material (ammonia or urea) canreact with the nitrogen oxides. A system that enabled the storage ofammonia (NH₃) without requiring storage under high pressure, so that theammonia could be directly injected into hot exhaust gasses and rapidlyreact with nitrogen oxides, would be of value.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a system isprovided for storing and injecting ammonia into the exhaust gasses of anengine, which enables safe storage of the ammonia and the injection ofammonia into the exhaust gasses for rapid reaction with nitrogen oxides.The ammonia is stored as a liquid mixture of ammonia and water. Theammonia is preferably stored as a mixture of between 30 and 70 grams ofammonia per 100 grams of water. The liquid mixture is drawn off througha tube leading from the container. In one system, the tube is heated bythe exhaust gasses and the mixture of ammonia and water is injecteddirectly into the exhaust gasses.

The novel features of the invention are set forth with particularity inthe appended claims. The invention will be best understood from thefollowing description when read in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic view of an engine, with pollutionreduction apparatus of the present invention installed therein.

FIG. 2 is a graph showing variation of the saturation mass of ammonia inwater as a function of temperature.

FIG. 3 is a graph similar to that of FIG. 2, but showing variation ofthe saturation percent (by mass) of ammonia in a mixture of ammonia andwater, as a function of temperature.

FIG. 4 is an enlarged view of a portion of the system of FIG. 1, showingseparation of a liquid mixture of ammonia and water into gaseous ammoniaand water vapor.

FIG. 5 is a sectional-view showing a portion of the apparatus of FIG. 2.

FIG. 6 is a simplified schematic view of a system of another embodimentof the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a system 10 of the present invention, wherein anengine 12 has cylinders in which fuel and air are combusted to turn acrankshaft 14. The combustion produces hot exhaust gasses that arepassed through an exhaust conduit 16 into the atmosphere. The exhaustconduit includes a manifold 20 that is connected to a few cylinders tocollect the exhaust gasses therefrom. A catalytic convertor 22 that liesalong the exhaust conduit, is widely used in vehicle engines to reducepollution.

FIG. 1 shows an ammonia injection system 30 that includes a source 32 ofammonia. An injector apparatus 33 includes a metering valve 34, tube 36with tube portion 62, and an injection nozzle at 40. The metering valve34 passes ammonia from the source through a tube 36 to an ammoniainjection location 40 where ammonia is injected into the exhaust conduit16 to mix with hot exhaust gasses. The location 40 lies in or close tothe exhaust gas manifold 20, so the ammonia encounters very hot exhaustgasses (usually over 1100° F. at high engine loads) to promote thereaction of ammonia and the exhaust gasses and thereby reduce nitrogenoxides.

In accordance with the present invention, the source 32 for ammonia is acontainer 50 that contains a mixture 70 of ammonia in water. FIG. 2includes a graph 52 showing the mass of ammonia, at saturation in asolution that contains 100 grams of water, at different temperatures.FIG. 3 contains a similar graph 54 that shows the saturation percent, bymass, of ammonia in a solution of ammonia and water. It can be seen thatthe percent ammonia (by mass), ranges from about 47% at 32° F. through33% ammonia at 72° F., down to 0% at 212° F. As a practical matter,applicant can vary the percent ammonia according to the weather, butprefers to establish about 25% ammonia, so the ammonia will not go outof the mixture unless the temperature of the mixture increases beyondabout 105° F. Also, the container is kept away from the engine and iscooled by air, to avoid heating the container. If the container shouldbe heated so that gaseous ammonia begins to accumulate under pressureand the pressure exceeds a certain limit (e.g. 2 psi), a relief valve 60(FIG. 1) will slowly vent the gaseous ammonia into the atmosphere. Therate of ammonia vented is very small, so it is not dangerous. A checkvalve 61 (FIG. 1) can admit air to avoid a vacuum above the liquid whenthe liquid is withdrawn.

The tube 36 that carries the ammonia-water mixture has a portion 62 thatis wrapped about the exhaust conduit 16, to rapidly heat theammonia-water mixture that passes through the tube 36 to the injectionlocation 40.

FIG. 4 indicates how the ammonia may be separated from the water at aseparation station 68, before injection of the ammonia into the exhaustconduit. Initially, the mixture 70 at a temperature such as 75° F.passes through the tube 36, to the tube portion 62 that is in aheat-exchange relationship with the exhaust conduit, so material withinthe tube portion 62 is rapidly heated. With the initial percent ofammonia being about 25%, the ammonia is not released as a gas until themixture reaches the location 72 which is at about 105° F. Progressivelymore ammonia is released as the temperature of the mixture progressivelyincreases. At the location 74, the mixture has a temperature of about200° F., and only a few percent of ammonia remains in the mixture. Therest of the ammonia, indicated at 80, continues along a tube end portion82, that carries the ammonia along a path 83 to an injector shown at 84in FIG. 4. The injector can be of the type described in our earlier U.S.Pat. No. 5,992,141, which results in rapid heating of the gaseousammonia prior to its injection into the very high temperature exhaustgasses, to activate the ammonia (break down some of the ammonia into itsconstituents) for injection into the exhaust gas stream.

The liquid 90 shown in FIG. 4 which moves along a path 91, contains onlya very small percent of ammonia, and is disposed of. One way to disposeof it, indicated in FIG. 1, is to carry the liquid with a very smallpercent of ammonia along a tube 92 for injection at 94 into the exhaustpipe. The location 94 is a location where the temperature of the exhaustgasses have been reduced to perhaps 250° F., in which case the smallquantity of injected water will evaporate and become part of the exhaustgas stream that is admitted into the atmosphere. It should be noted thatsmall pumps may be located in the injection system 30 where pressureincreases are required. In FIG. 1, the metering valve 34 is controlledby a circuit 100 that also controls a fuel injector 102 that injectsfuel from a fuel line 104 into the engine cylinders. As discussed in myearlier U.S. Pat. No. 5,992,141, this varies the amount of ammonia inaccordance with the load on the engine, to more effectively neutralizenitrogen oxides.

FIG. 6 illustrates a system 110 which includes a container 112 thatcontains the mixture 70 of ammonia (NH₃) and water (HO₂). Otheringredients can be added to the mixture 70, but applicant prefers thatmost of the mixture be water and ammonia. The ammonia is required toreduce nitrogen oxides and the water is useful to retain the ammonia andis a liquid that is easily disposed of because of its benigncharacteristics. In the system 110 of FIG. 6, applicant passes themixture 70, which may have perhaps 25% ammonia by weight, and water,directly through a nozzle 84 that lies in the exhaust gas conduits 16,at an upstream location near or in the exhaust manifold. This system hasthe disadvantage that water is injected with the ammonia into the hotexhaust gasses, and tends to cool the exhaust gasses more rapidly.However, the amount of water and ammonia is very small, so the coolingeffect of the water is very small. This system also has the disadvantagethat the ammonia is heated only moderately by the hot nozzle prior toinjection into the exhaust gas stream, so only a low percent of theammonia is activated to break down the ammonia into its components (NH₂and NH) prior to injection. However, the simplicity of the system 110can make it useful even if its effectiveness in reducing nitrogen oxidesis not as great.

Thus, the invention provides a system for reducing nitrogen oxides inthe exhaust gasses of an engine by the injection of ammonia into theexhaust gasses, which facilitates storage of the ammonia. The ammonia isstored as a mixture of ammonia and water (other liquids can be present),with the percent of ammonia preferably being between about 15% and 50%to avoid the generation of pressured ammonia gas. In one system, themixture is heated to convert most of the ammonia into its gaseous stateand separate it from the water that still remains liquid, and with thegaseous ammonia being further heated to activate at least a portion ofit and then being injected into the hot exhaust gasses near or in theexhaust gas manifold. In a simpler system, the ammonia and water mixture15 flowed towards the exhaust gas conduit and both ammonia and water areinjected into the exhaust conduit.

Although particular embodiments of the invention have been described andillustrated herein, it is recognized that modifications and variationsmay readily occur to those skilled in the art, and consequently, it isintended that the claims be interpreted to cover such modifications andequivalents.

1. In an engine which includes means for combusting hydrocarbons in airto produce work wherein said means also produces a stream of exhaustgasses that contain nitrogen oxides, with the engine having an exhaustconduit through which the exhaust gasses are passed before being emittedinto the atmosphere, the improvement comprising: a container; a liquidmixture of ammonia and water in said container, said container beingstored away from said means for combusting to minimize heating; aninjector apparatus coupled to said liquid in said container and to saidexhaust conduit, said injector apparatus being constructed to inject atleast ammonia of said mixture into said exhaust conduit.
 2. The enginedescribed in claim 1 wherein: said mixture of ammonia and water in saidcontainer includes about 25% ammonia and about 75% water.
 3. The enginedescribed in claim 1 wherein: said injector apparatus includes a tubethat carries said liquid mixture, said tube lying in a heat-exchangerelationship with said exhaust conduit to use the heat of the exhaustgasses to heat the liquid mixture of ammonia and water.
 4. The enginedescribed in claim 1 wherein: said injector apparatus includes a tubethat carries said mixture of ammonia and water from said source, and anozzle coupled to said tube, said injector apparatus being constructedto inject said mixture of ammonia and water through said nozzle intosaid exhaust conduit.
 5. In an engine which has an engine block withcylinders where hydrocarbons are combusted in air to produce work, andwhich has an exhaust conduit that carries away a stream of exhaustgasses that contain nitrogen oxides, a source of ammonia and aninjection apparatus that is coupled to said source and that injectsammonia into the conduit to reduce nitrogen oxides, the improvementwherein: said source of ammonia comprises a container and a liquidmixture of ammonia and water in said container, said container beingthermally isolated from said engine block and said exhaust conduit. saidinjection apparatus is constructed to inject ammonia and at least someof the water into said exhaust conduit.
 6. The engine described in claim5 wherein: said injector apparatus includes a tube that carries saidliquid mixture and that lies in a heat-exchange relationship with saidexhaust conduit to use the heat of the exhaust gasses to heat themixture of ammonia and water.
 7. The engine described in claim 5wherein: said mixture of ammonia and water in said container includesabout 25% ammonia and 75% water.
 8. A method for reducing nitrogen oxideemission from an engine that has an engine block with cylinders wherehydrocarbons are combusted in air to produce work, and which has anexhaust conduit that carries away a stream of exhaust gasses thatcontain nitrogen oxides, comprising: storing a liquid mixture of ammoniaand water in a container while thermally isolating the container fromsaid engine block and said exhaust conduit; passing said mixture fromsaid container to an injector apparatus, and injecting ammonia and waterinto said exhaust conduit at a location downstream of said engine block.